Bulletin of Environment, Pharmacology and Life Sciences Online ISSN 2277-1808 Bull. Env. Pharmacol. Life Sci. Volume 2 [2] January 2013: 52- 63

Review Article

© 2012, Academy for Environment and Life Sciences, HAEMATOPOIETIC PROPERTIES OF India Website: www.bepls.com

Use of Plant Species in Controlling Environmental Pollution- A Review S. Ramesh Kumar1*, T. Arumugam2, C.R. Anandakumar3, S. Balakrishnan4 and D.S. Rajavel5 Professor, Department of Horticulture, Vanavarayar Institute of Agriculture, Manakkadavu, Pollachi, TNAU, Tamil Nadu, India. 2and4Professor, Department of Horticulture, 3Professor, Department of Plant Breeding and Genetics, 5Professor, Department of Agricultural Entomology, Agricultural College and Research Institute, TNAU, Madurai, Tamil Nadu, India. *Corresponding author E-mail: [email protected] 1*Assistant

ABSTRACT Plants in urban areas play an essential role to cleanse the pollution in human environment. The paper describes the choice of eco–friendly plant species and their right placement in the urban environment to overcome the pollution problems. Key words: Pollution, trees, shrubs, phytoremediation

INTRODUCTION In modern times pollution has become the biggest menace for the survival of the biological species. There are various types of pollution e.g. air, water, soil, sound and mental pollution. Earth was a beautiful landscape but man has ruthlessly exploited for his greed specially, in the last century. With rapid industrialization and random urbanization environmental pollution has become a serious problem. Over exploitation of open spaces, ever-increasing number of automobiles and demographic pressure has further aggravated the problem. There are various ways and means to mitigate the urban environmental pollution. Plan-ting of trees and shrubs for abatement of pollution and improvement of environment is an effective way and well recognized throughout the world. Earlier, the purpose of planting trees in urban areas was purely aesthetic [1]. The incessant increase of urban environmental pollution has necessitated to reconsider the whole approach of urban landscaping and its orientation in order to achieve duel effect i.e. bio-aesthetics and mitigation of pollution. Proper planning and planting scheme depending upon the magnitude and type of pollution, selection of pollution- tolerant and dust scavenging trees and shrubs should be done for bioremediation of urban environmental pollution. Pollution, the major problem in cities, is compounded by the fact that there is no exhaust for the polluted air to escape. Landscape architects can solve the pollution problems related to urban landscape by creating a micro-climate [2]. Pollution Pollution is defined as ‘an undesirable change in physical, chemical and biological characteristics of air, water and land that may be harmful to living organisms, living conditions and cultural assets. The pollution control board defined pollution as unfavourable alteration of our surrounding, largely as a byproduct of human activities. The pollution may be due to human activities or natural ecosystems [3]. Natural pollution contaminates the air by storms, forest fire, volcanoes and natural processes (methane from marshy lands). Nature by and large treats, recycles and makes good use of the pollutants and renders them less harmful, whereas man-made pollutants threaten the integrity of the nature. Pollutants The substances, which cause pollution, are called pollutants. Pollutant is defined as any substance that is released intentionally or inadvertently by man into the environment in such a concentration that may have adverse effect on environmental health [4]. Environment Protection Act, 1986 EPA, 1986) defines pollutant, as any solid, liquid or gaseous substance present in such a concentration as may be, or tend to be, injurious to environment. Air Pollution Air is necessary for the survival of all higher forms of life on earth. On an average, a person needs at least 30 lb of air every day to live, but only about 3 lb of water and 1.5 lb of food. A person can live about 5 weeks without food and about 5 days without water, but only 5 minutes without air. Naturally, BEPLS Vol 2 [2] January 2013

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every one likes to breathe fresh, clean air. But the atmosphere, that invisible yet essential ocean of different gases called air, is as susceptible to pollution from human activities as are water and land environments [5]. According to the WHO report, about 10 to 15 % of the total population of India is suffering from common cold, bronchitis, asthma, hay fever etc. These diseases are no doubt airborne and spread the infection from several hundred kilometers under favourable atmospheric conditions. Dust and soot in the air contribute to between 20 and 200 deaths each day in America’s biggest cities. Ill health from microscopic particulates with tiny specks smaller than the width of a human hair can lodge deep in the lungs and are associated with respiratory diseases, heart attacks and premature deaths. The new research indicates elderly people suffer the most harm. In the United States the Environmental Protection Agency (EPA) currently sets the maximum allowable concentration of microscopic particles at 150 μm/m3 of air. The air is being continuously polluted in urban areas through heavy traffic, industry, domestic fuel combustion, stone quarries, coalmines and various agricultural activities from the adjoining areas. These particulates are no doubt dangerous to human health and environment causing various diseases to plants and animals, damage to properties including our cultural heritage, national monuments, archives etc. Dust concentration varies from place to place and hour to hour, diurnally depending upon traffic, type of industry etc. The highest dust concentration tends to be in summer, reaching maximum during mid-day and late–afternoon. In some large cities where wind and temperature fall more steadily, the concentration of dust also reduces accordingly. Criteria air pollutants The five primary criteria pollutants include the gases- sulfur dioxide (SO2), nitrogen oxides (NOx) and carbon monoxide (CO), solid or liquid particulates (smaller than 10 µm), and particulate lead. EFFECTS OF DIFFERENT TYPES OF AIR POLLUTANTS According to Agarwal [6], air pollution is broad term, which actually covers lots of different types of problems. They are, acid rain, domestic and industrial smoke, smog, greenhouse effect, particulates, radionuclides and ozone layer depletion. Plant species for pollution control While selecting the species for pollution control the following are the important characteristics could be considered. Plants should be evergreen, large leaved, rough bark, indigenous, ecologically compatible, low water requirement, minimum care, high absorption of pollutants, resistant pollutants, agro-climatic suitability, height and spread, Canopy architecture, Growth rate and habit (straight undivided trunk), Aesthetic effect (foliage, conspicuous and attractive flower colour), Pollution tolerance and dust scavenging capacity. Thick plantations – small filtering effects

Loose plantations – good filtering effects

Morphological feature of plant leaves for dust capture efficiency

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Different types of leaves tend to have differences in several aspects of their surfaces. Some types of leaves have greater surface rigidity or roughness than other leaves, which may affect their stickiness or particle solubility. Stickier leaves are better for collecting particles because more particles would stick to their surface. Therefore, certain plant leaves may be more useful for efficient dust capturing than other plants. The various morphological features are also major factors for dust capturing by leaves. The crown area of plants is depending upon the morphological features of the leaf [7]. The various types of Morphological features viz. shape, size and surface texture of leaf are discussed below: Leaves can be of many different shapes. Primarily, leaves are divided into simple – a single leaf blade with a bud at the base of the leaf stems; or compound leaf - a leaf with more than one blade. All blades are attached to a single leaf stem. Where the leaf stems attaches to the twig with an axial bud.

Compound leaf

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Simple Leaf

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Compound leaves may be palmate - having the leaflets arranged round a single point like fingers on the palm of a hand; or pinnate - when the leaves are joined on the two sides of the stalk, like the vanes of a feather. The form of leaves is related with all their functions and their environment. In addition to photosynthesis, the leaf also carries out other exchanges with the atmosphere. It is through the leaf that the plant "breathes" (absorbs oxygen and releases carbon dioxide and generate energy) and transpires. Epidermic tissues in the leaf contain stomata - microscopic openings like valves which regulate opening or closing, permitting or preventing transpiration, through which the plant loses the major part of the water it absorbs so as to allow further absorption by the roots. In most plants the stomata are located on the underside of the leaves. Their function is regulated so that plants living in dry climates have a substantially smaller number of stomata than those in humid climates, where stomata are numerous and prominent. Where humidity is low the stomata may actually be recessed or partly protected by soft hairs which can prevent excessive transpiration. Choice of eco-friendly plant species in urban environment to mitigate airborne particulate pollution During tree plantation in an urban environment little or no attention has been paid to evaluate the effect of trees on filtering the particulate matter. New housing developments offer an opportunity to control atmospheric particulate pollution through tree plantations. Trees such as Tamarind (Tamarindus indicus) having smaller compound leaves are generally more efficient particle collectors than larger leaves. Particle deposition is heaviest at the leaf tip and along leaf margin. In the preliminary survey of dust fall on common roadside trees in Mumbai, carried out by Shetye and Chaphekar [8] reported that the shape of leaves of Mango (Mangifera indica), Ashoka (Polyalthea longifolia), Pongamia (Derris indica) and Umbrella (Thespepsia populnea) trees captured higher amounts of dust as compared to other neighboring plants. Dochinger [9], a plant pathologist of USDA Forest Service, Ohio, reported that the filtering effects of evergreen trees are better than the deciduous trees. In Singapore; it has been noted that a single row of trees planted with or without shrubs can reduce particulate matter by 25% and each hectare (2.471 acres) of plantation can produce enough oxygen to keep about 45 persons alive [1]. The value of trees in urban environment is now generally recognized not only aesthetically but also functionally in helping to make cities and towns agreeable places to live and work in. The first choice should be, therefore, to select easily propagated and readily available, medium growing, ecologically much suitable, pest and disease resistant tree species and also require less maintenance should be given top priority. Columnar and medium-sized trees are preferred. Ingold [10] reported that the leaves with complex shapes and large circumference area reported to be collected particles more efficiently. Many trees like Neem (Azadirchta indica), Silk cotton (Bombax ceiba), Indian laburnum (Cassia fistula and C. siamea), Gulmohar (Delonix regia), Pipal (Ficus religiosa), Jacaranda (Jacaranda mimosifolia), Indian lilac (Lagerstroemia indica), Temple or Pagoda tree (Plumeria rubra and P. alba), Java plum (Syzygium cumini) and several other roadside and street trees have found more suitable in urban environment [11-14]. If such trees are to be planted, their local ecological relationship with human environment has to be studied properly. It should be borne in mind that these trees may cause allergic disorders such as hay fever; asthma and toxemia due to airborne pollen grains, which can also contribute to atmospheric pollution significantly. Chakre [15] has suggested that the insect-pollinated trees with short flowering periods and also with less pollen productivity should be BEPLS Vol 2 [2] January 2013

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selected. It is also recommended that wind-pollinated tree species those, flowering during rainy season can also be planted, as rains will wash out extra pollens. A tree should be relatively free of insects and diseases and there should not be dropping of messy fruits (Muntingia calabura, Cerbera odolam ), seed pods (Acacia auriculaeformis), twigs and leaves (Dyera costulata). Trees with a tendency to drop large and heavy fruits (Durio spp.) and emit bad smell (Sterculia foetida) must be considered a serious drawback. Table 1. Plant species (deciduous) arranged in the decreasing order of their air pollution tolerance index Plant species

T

P

A

R

APTI

Albizzia lebbeck

8.00

6.3

18.00

53

32

Cassia fistula

6.89

6.2

16.00

72

28

Zizyphus jujuuba

10.26

6.0

10.60

80

25

Azadirachta indica

7.50

6.3

10.21

77

22

Ficus religiosa

14.86

8.0

4.78

87

20

Psidium guajava

7.13

6.3

7.78

73

18

Phyllanthus emblica

10.00

6.0

4.27

75

14

Tamaridus indica

4.879

4.0

6.00

85

14

Moringa olifera

6.60

6.2

2.50

87

12

Delaonix regia

6.27

6.4

2.00

45

7

Tectona grandis

4.50

7.3

1.35

54

6

Morus alba

6.00

6.7

1.00

40

5

Source: Agarwal (2006) T = total chlorophyll (mg g-1 of dry weight); A= ascorbic acid (mg g-1 of fresh weight); P= leaf extract pH; R= relative water content (%). Table 2. Plant species (evergreen) arranged in decreasing order of their air pollution tolerant index Plant species

T

P

A

R

APTI

Pithecolobium dulce

16.41

6.0

7.05

87

24

Ficus benghalensis

6.94

8.0

7.49

79

19

Polyalthia longifolia Terminalia arjuna Leucana leucocephala

5.78 4.86 12.50

6.2 6.1 5.8

8.68 7.98 5.80

80 75 86

18 16 19

Eucalyptus citriodora

4.25

5.0

4.49

80

12

Acacia Arabica

4.54

6.5

5.98

79

15

Mangifera indica

4.28

5.4

3.78

87

12

Annona squamosa 4.00 5.6 3.75 71 10 Casuarina equisetifolia 0.75 5.4 2.59 58 5 Source: Chakre (2006) T = total chlorophyll (mg g-1 of dry weight); A= ascorbic acid (mg g-1 of fresh weight); P= leaf extract pH; R= relative water content (%).

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Table 3. Plant species (shrubs) arranged in decreasing order of their air pollution tolerant index Plant species

T

P

A

R

APTI

Bougainvillea spectabilis

11.70

6.1

12.39

74

30

Calotropis gigantes

13.00

6.4

9.00

94

27

Poinsettia sp.

17.10

6.0

7.00

80

24

Ricinus communis

17.20

6.2

5.00

93

21

Citrus lemon

6.68

6.0

6.25

74

15

Lantana indica

7.51

7.6

4.63

65

14

Rosa indica

4.50

5.5

4.75

74

12

Source: Mark (1997) Water pollution Water has such a strong tendency to dissolve other substances and sometimes referred to as the universal solvent.This is largely because of its polar molecular structure. Pure water, that is, pure H2O, is not found under natural conditions in streams, lakes, ground water, or the oceans. It always has something dissolved or suspended in it. Because of this, there is not any definite line of demarcation between clean water and contaminated water. n general terms, water is considered to be polluted when it contains enough foreign material to render it unfit for specific beneficial use, such as for drinking, recreation, or fish propagation. Actually human activity is the cause of the poor water quality and cause water pollution. Vegetative filter strips for water pollution control in agriculture Orchards, vineyards, and row crops have the greatest erosion rates in irrigated agriculture, especially those that are managed with bare soil between tree or vine rows. The vegetative filter strip (VFS) offers one way to control erosion rates and keep soil in the field rather than letting it be carried off site in drainage water. A VFS is an area of vegetation that is planted intentionally to help remove sediment and other pollutants from runoff water [16]. Key design elements for vegetative filter strips The United States Environmental Protection Agency (EPA) encourages growers to use engineered vegetative treatment systems such as VFSs at sites where these systems are likely to bring about a significant reduction in nonpoint source (NPS) pollution [17]. You can establish VFSs downslope from crop fields or animal production sites to control NPS pollutants that would otherwise escape with runoff. In orchards, you can use multiple VFSs installed perpendicular to the direction of surface water runoff to reduce soil erosion and even avoid expenses associated with herbicide application. The strips also have the potential to reduce the level of some pesticides in runoff by enhancing water infiltration and retention in the field. For example, con- taminants such as phosphorus and certain pesticides such as pyrethroids that bind strongly to soil particles get trapped and retained in VFSs. Pollutant-filtering mechanisms of vegetative filter strips A vegetative filter strip functionally consists of three distinct layers surface vegetation, root zone, and subsoil horizon and as a result, the flow of water and pollutants through the filter strip can be a complex process. Once surface flow enters a VFS, infiltration is followed by saturation of the shallow subsurface. When the inflow rate exceeds the strip’s infiltration capacity, overland flow occurs. In the root zone, some water infiltrates deeper into the subsoil while the remainder becomes lateral subsurface flow or interflow. Runoff is less from hill slopes that have VFSs than from those that have none, a result of increased infiltration rates in the vegetated area. The vegetative strip’s root zone allows high infiltration rates via macropores that arise with the generally improved soil structure created by plant roots and other biological activities. The most important pollutant-trapping mechanism of VFSs is infiltration, followed by storage in the surface layer. The soil constituent with the greatest influence on pesticide transport or pollutant retention and degradation is organic matter in the root zone and overlying surface litter layer. Greater biological activity in a soil improves its ability to effectively deals with pesticides and pollutants, and that kind of activity is more prevalent in a soil rich in plant roots, soil micro- and macro-fauna, and bacteria than in a soil without those organisms. Soil microorganisms play an essential role in the degradation of contaminants and soil organic matter is chemically reactive with BEPLS Vol 2 [2] January 2013

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the contaminants. For these reasons, you can expect degradation and adsorption of herbicides and pesticides to be greater in the filter strip’s root zone than in adjacent fallow soils. Vegetative filter strips on sloping land are subject to horizontal interflow within the root zone, in which case some pesticides may be filtered out, adsorbing onto soil organic matter. When the interflow water reappears on the surface as return flow it may have a lower pesticide concentration than the water that has flowed above ground. When infiltration is high in a VFS, the microbial- and plant-uptake processes cause denitrification, degradation of chemicals, and reduction of chemical concentrations in the surface layer between runoff events. The effectiveness of VFSs depends on field conditions such as soil type, rainfall intensity, slope, microtopography (surface soil roughness), the infiltration capacity of the vegetated area, the width of the strip, and the height of its plants. Slope and micro-topography affect overland flow velocity and uniformity and also appear to have an effect on the ability of VFSs to retain sediment and pollutants in runoff. Of course, the steeper the slope, the greater the sediment yield, all other factors being equal. Infiltration capacity and interflow within the VFSs influence the fate and path of dissolved nutrients and chemicals. The width of VFSs determines the strips’ sediment removing capacity and the amount of time the pollutant can be expected to remain in soil layers where adsorption and degradation processes are active. Aquatic plants for removal of pollutants (Pb, Cu, Cd, Fe, hg and chromium) from leather industries Hydrilla verticillata;Spirodela polyrrhiza; Bacopa monnierii; Phragmites karka; Scirpus lacustris; Water hyacinth (Eichhornia crassipes); Pennywarth (Hydrocotyle umbellate; Duck weed (Lemna minor; Water velvet (Azolla pinnata) Soil pollution The introduction of substances, biological organisms, or energy into the soil, resulting in a change of the soil quality, which is likely to affect the normal use of the soil or endangering public health and the living environment. Phytoremediation Phytoremediation is the use of living green plants for in situ risk reduction and/or removal of contaminants from contaminated soil, water, sediments, and air. Specially selected or engineered plants are used in the process. Risk reduction can be through a process of removal, degradation of, or containment of a contaminant or a combination of any of these factors. Phytoremediation is an energy efficient, aesthically pleasing method of remediating sites with low to moderate levels of contamination and it can be used in conjuction with other more traditional remedial methods as a finishing step to the remedial process. One of the main advantages of phytoremediation is that of its relatively low cost compared to other remedial methods such as excavation. The cost of phytoremediation has been estimated as $25 - $100 per ton of soil, and $0.60 - $6.00 per 1000 gallons of polluted water with remediation of organics being cheaoer than remediation of metals. In many cases phytoremediation has been found to be less than half the price of alternative methods. Phytoremediation also offers a permanent in situ remediation rather than simply translocating the problem. However phytoremediation is not without its faults, it is a process which is dependent on the depth of the roots and the tolerance of the plant to the contaminant. Exposure of animals to plants which act as hyperaccumulators can also be a concern to environmentalists as herbivorous animals may accumulate contaminate particles in their tissues which could in turn affect a whole food web. Phytoremediation is actually a genneric term for several ways in which plants can be used to clean up contaminated soils and water. Plants may break down or degrade organic pollutants, or remove and stabilize metal contaminants. This may be done through one of or a combination of the methods described in the next chapter. The methods used to phytoremediate metal contaminants are slightly different to those used to remediate sites polluted with organic contaminants. METHODS OF PHYTOREMEDIATION Phytoextraction (Phytoaccumulation) Phytoextraction, the use of plants to remove contaminants from soil by accumulation of contaminants in plant tissue, is a promising cleanup technology for a variety of metal-containing soils [18,19]. However, hytoextrac- uption of high specific activity radionuclides such as 137Cs or 90Sr is a challenge because of the very low molar reconcentrations of the radionuclide in soil (typically in weapthe order of 10_12 mol/kg) compared with much higher effecconcentrations of stable elements naturally present in soil. In BEPLS Vol 2 [2] January 2013

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addition, plant uptake of 137Cs and 90Sr can be inhibited by competition with K [20] and Ca [21], respectively. Further, the pros-pect of phytoextraction of 137Cs from contaminated soil is minimized because sorption of Cs into interlayer spaces on mica–illite minerals appears to be highly spe-cific and poorly reversible [22,23]. Many metals such as Zn, Mn, Ni, and Cu are essential micronutrients. In common nonaccumulator plants, accumulation of these micronutrients does not exceed their metabolic needs (